/**
 * @file
 * This is the IPv4 layer implementation for incoming and outgoing IP traffic.
 *
 * @see ip_frag.c
 *
 */

/*
 * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 *
 * Author: Adam Dunkels <adam@sics.se>
 *
 */

#include "lwip/opt.h"
#include "lwip/ip.h"
#include "lwip/def.h"
#include "lwip/mem.h"
#include "lwip/ip_frag.h"
#include "lwip/inet_chksum.h"
#include "lwip/netif.h"
#include "lwip/icmp.h"
#include "lwip/igmp.h"
#include "lwip/raw.h"
#include "lwip/udp.h"
#include "lwip/tcp_impl.h"
#include "lwip/snmp.h"
#include "lwip/dhcp.h"
#include "lwip/autoip.h"
#include "lwip/stats.h"
#include "arch/perf.h"

#include <string.h>

/** Set this to 0 in the rare case of wanting to call an extra function to
 * generate the IP checksum (in contrast to calculating it on-the-fly). */
#ifndef LWIP_INLINE_IP_CHKSUM
#define LWIP_INLINE_IP_CHKSUM 1
#endif
#if LWIP_INLINE_IP_CHKSUM && CHECKSUM_GEN_IP
#define CHECKSUM_GEN_IP_INLINE 1
#else
#define CHECKSUM_GEN_IP_INLINE 0
#endif

#if LWIP_DHCP || defined(LWIP_IP_ACCEPT_UDP_PORT)
#define IP_ACCEPT_LINK_LAYER_ADDRESSING 1

/** Some defines for DHCP to let link-layer-addressed packets through while the
 * netif is down.
 * To use this in your own application/protocol, define LWIP_IP_ACCEPT_UDP_PORT
 * to return 1 if the port is accepted and 0 if the port is not accepted.
 */
#if LWIP_DHCP && defined(LWIP_IP_ACCEPT_UDP_PORT)
/* accept DHCP client port and custom port */
#define IP_ACCEPT_LINK_LAYER_ADDRESSED_PORT(port)                                                                      \
	(((port) == PP_NTOHS(DHCP_CLIENT_PORT)) || (LWIP_IP_ACCEPT_UDP_PORT(port)))
#elif defined(LWIP_IP_ACCEPT_UDP_PORT) /* LWIP_DHCP && defined(LWIP_IP_ACCEPT_UDP_PORT) */
/* accept custom port only */
#define IP_ACCEPT_LINK_LAYER_ADDRESSED_PORT(port) (LWIP_IP_ACCEPT_UDP_PORT(port))
#else /* LWIP_DHCP && defined(LWIP_IP_ACCEPT_UDP_PORT) */
/* accept DHCP client port only */
#define IP_ACCEPT_LINK_LAYER_ADDRESSED_PORT(port) ((port) == PP_NTOHS(DHCP_CLIENT_PORT))
#endif /* LWIP_DHCP && defined(LWIP_IP_ACCEPT_UDP_PORT) */

#else /* LWIP_DHCP */
#define IP_ACCEPT_LINK_LAYER_ADDRESSING 0
#endif /* LWIP_DHCP */

/**
 * The interface that provided the packet for the current callback
 * invocation.
 */
struct netif *current_netif;

/**
 * Header of the input packet currently being processed.
 */
const struct ip_hdr *current_header;
/** Source IP address of current_header */
ip_addr_t current_iphdr_src;
/** Destination IP address of current_header */
ip_addr_t current_iphdr_dest;

/** The IP header ID of the next outgoing IP packet */
static u16_t ip_id;

/**
 * Finds the appropriate network interface for a given IP address. It
 * searches the list of network interfaces linearly. A match is found
 * if the masked IP address of the network interface equals the masked
 * IP address given to the function.
 *
 * @param dest the destination IP address for which to find the route
 * @return the netif on which to send to reach dest
 */
struct netif *ip_route(ip_addr_t *dest)
{
	struct netif *netif;

#ifdef LWIP_HOOK_IP4_ROUTE
	netif = LWIP_HOOK_IP4_ROUTE(dest);
	if (netif != NULL) {
		return netif;
	}
#endif

	/* iterate through netifs */
	for (netif = netif_list; netif != NULL; netif = netif->next) {
		/* network mask matches? */
		if (netif_is_up(netif)) {
			if (ip_addr_netcmp(dest, &(netif->ip_addr), &(netif->netmask))) {
				/* return netif on which to forward IP packet */
				return netif;
			}
		}
	}
	if ((netif_default == NULL) || (!netif_is_up(netif_default))) {
		LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
		            ("ip_route: No route to %" U16_F ".%" U16_F ".%" U16_F ".%" U16_F "\n",
		             ip4_addr1_16(dest),
		             ip4_addr2_16(dest),
		             ip4_addr3_16(dest),
		             ip4_addr4_16(dest)));
		IP_STATS_INC(ip.rterr);
		snmp_inc_ipoutnoroutes();
		return NULL;
	}
	/* no matching netif found, use default netif */
	return netif_default;
}

#if IP_FORWARD
/**
 * Determine whether an IP address is in a reserved set of addresses
 * that may not be forwarded, or whether datagrams to that destination
 * may be forwarded.
 * @param p the packet to forward
 * @param dest the destination IP address
 * @return 1: can forward 0: discard
 */
static int ip_canforward(struct pbuf *p)
{
	u32_t addr = ip4_addr_get_u32(ip_current_dest_addr());

	if (p->flags & PBUF_FLAG_LLBCAST) {
		/* don't route link-layer broadcasts */
		return 0;
	}
	if ((p->flags & PBUF_FLAG_LLMCAST) && !IP_MULTICAST(addr)) {
		/* don't route link-layer multicasts unless the destination address is an IP
		   multicast address */
		return 0;
	}
	if (IP_EXPERIMENTAL(addr)) {
		return 0;
	}
	if (IP_CLASSA(addr)) {
		u32_t net = addr & IP_CLASSA_NET;
		if ((net == 0) || (net == (IP_LOOPBACKNET << IP_CLASSA_NSHIFT))) {
			/* don't route loopback packets */
			return 0;
		}
	}
	return 1;
}

/**
 * Forwards an IP packet. It finds an appropriate route for the
 * packet, decrements the TTL value of the packet, adjusts the
 * checksum and outputs the packet on the appropriate interface.
 *
 * @param p the packet to forward (p->payload points to IP header)
 * @param iphdr the IP header of the input packet
 * @param inp the netif on which this packet was received
 */
static void ip_forward(struct pbuf *p, struct ip_hdr *iphdr, struct netif *inp)
{
	struct netif *netif;

	PERF_START;

	if (!ip_canforward(p)) {
		goto return_noroute;
	}

	/* RFC3927 2.7: do not forward link-local addresses */
	if (ip_addr_islinklocal(&current_iphdr_dest)) {
		LWIP_DEBUGF(IP_DEBUG,
		            ("ip_forward: not forwarding LLA %" U16_F ".%" U16_F ".%" U16_F ".%" U16_F "\n",
		             ip4_addr1_16(&current_iphdr_dest),
		             ip4_addr2_16(&current_iphdr_dest),
		             ip4_addr3_16(&current_iphdr_dest),
		             ip4_addr4_16(&current_iphdr_dest)));
		goto return_noroute;
	}

	/* Find network interface where to forward this IP packet to. */
	netif = ip_route(&current_iphdr_dest);
	if (netif == NULL) {
		LWIP_DEBUGF(IP_DEBUG,
		            ("ip_forward: no forwarding route for %" U16_F ".%" U16_F ".%" U16_F ".%" U16_F " found\n",
		             ip4_addr1_16(&current_iphdr_dest),
		             ip4_addr2_16(&current_iphdr_dest),
		             ip4_addr3_16(&current_iphdr_dest),
		             ip4_addr4_16(&current_iphdr_dest)));
		/* @todo: send ICMP_DUR_NET? */
		goto return_noroute;
	}
#if !IP_FORWARD_ALLOW_TX_ON_RX_NETIF
	/* Do not forward packets onto the same network interface on which
	 * they arrived. */
	if (netif == inp) {
		LWIP_DEBUGF(IP_DEBUG, ("ip_forward: not bouncing packets back on incoming interface.\n"));
		goto return_noroute;
	}
#endif /* IP_FORWARD_ALLOW_TX_ON_RX_NETIF */

	/* decrement TTL */
	IPH_TTL_SET(iphdr, IPH_TTL(iphdr) - 1);
	/* send ICMP if TTL == 0 */
	if (IPH_TTL(iphdr) == 0) {
		snmp_inc_ipinhdrerrors();
#if LWIP_ICMP
		/* Don't send ICMP messages in response to ICMP messages */
		if (IPH_PROTO(iphdr) != IP_PROTO_ICMP) {
			icmp_time_exceeded(p, ICMP_TE_TTL);
		}
#endif /* LWIP_ICMP */
		return;
	}

	/* Incrementally update the IP checksum. */
	if (IPH_CHKSUM(iphdr) >= PP_HTONS(0xffffU - 0x100)) {
		IPH_CHKSUM_SET(iphdr, IPH_CHKSUM(iphdr) + PP_HTONS(0x100) + 1);
	} else {
		IPH_CHKSUM_SET(iphdr, IPH_CHKSUM(iphdr) + PP_HTONS(0x100));
	}

	LWIP_DEBUGF(IP_DEBUG,
	            ("ip_forward: forwarding packet to %" U16_F ".%" U16_F ".%" U16_F ".%" U16_F "\n",
	             ip4_addr1_16(&current_iphdr_dest),
	             ip4_addr2_16(&current_iphdr_dest),
	             ip4_addr3_16(&current_iphdr_dest),
	             ip4_addr4_16(&current_iphdr_dest)));

	IP_STATS_INC(ip.fw);
	IP_STATS_INC(ip.xmit);
	snmp_inc_ipforwdatagrams();

	PERF_STOP("ip_forward");
	/* don't fragment if interface has mtu set to 0 [loopif] */
	if (netif->mtu && (p->tot_len > netif->mtu)) {
		if ((IPH_OFFSET(iphdr) & PP_NTOHS(IP_DF)) == 0) {
#if IP_FRAG
			ip_frag(p, netif, ip_current_dest_addr());
#else  /* IP_FRAG */
		/* @todo: send ICMP Destination Unreacheable code 13 "Communication administratively prohibited"? */
#endif /* IP_FRAG */
		} else {
			/* send ICMP Destination Unreacheable code 4: "Fragmentation Needed and DF Set" */
			icmp_dest_unreach(p, ICMP_DUR_FRAG);
		}
		return;
	}
	/* transmit pbuf on chosen interface */
	netif->output(netif, p, &current_iphdr_dest);
	return;
return_noroute:
	snmp_inc_ipoutnoroutes();
}
#endif /* IP_FORWARD */

/**
 * This function is called by the network interface device driver when
 * an IP packet is received. The function does the basic checks of the
 * IP header such as packet size being at least larger than the header
 * size etc. If the packet was not destined for us, the packet is
 * forwarded (using ip_forward). The IP checksum is always checked.
 *
 * Finally, the packet is sent to the upper layer protocol input function.
 *
 * @param p the received IP packet (p->payload points to IP header)
 * @param inp the netif on which this packet was received
 * @return ERR_OK if the packet was processed (could return ERR_* if it wasn't
 *         processed, but currently always returns ERR_OK)
 */
err_t ip_input(struct pbuf *p, struct netif *inp)
{
	struct ip_hdr *iphdr;
	struct netif * netif;
	u16_t          iphdr_hlen;
	u16_t          iphdr_len;
#if IP_ACCEPT_LINK_LAYER_ADDRESSING
	int check_ip_src = 1;
#endif /* IP_ACCEPT_LINK_LAYER_ADDRESSING */

	IP_STATS_INC(ip.recv);
	snmp_inc_ipinreceives();

	/* identify the IP header */
	iphdr = (struct ip_hdr *)p->payload;
	if (IPH_V(iphdr) != 4) {
		LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_WARNING,
		            ("IP packet dropped due to bad version number %" U16_F "\n", IPH_V(iphdr)));
		ip_debug_print(p);
		pbuf_free(p);
		IP_STATS_INC(ip.err);
		IP_STATS_INC(ip.drop);
		snmp_inc_ipinhdrerrors();
		return ERR_OK;
	}

#ifdef LWIP_HOOK_IP4_INPUT
	if (LWIP_HOOK_IP4_INPUT(p, inp)) {
		/* the packet has been eaten */
		return ERR_OK;
	}
#endif

	/* obtain IP header length in number of 32-bit words */
	iphdr_hlen = IPH_HL(iphdr);
	/* calculate IP header length in bytes */
	iphdr_hlen *= 4;
	/* obtain ip length in bytes */
	iphdr_len = ntohs(IPH_LEN(iphdr));

	/* header length exceeds first pbuf length, or ip length exceeds total pbuf length? */
	if ((iphdr_hlen > p->len) || (iphdr_len > p->tot_len)) {
		if (iphdr_hlen > p->len) {
			LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
			            ("IP header (len %" U16_F ") does not fit in first pbuf (len %" U16_F "), IP packet dropped.\n",
			             iphdr_hlen,
			             p->len));
		}
		if (iphdr_len > p->tot_len) {
			LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
			            ("IP (len %" U16_F ") is longer than pbuf (len %" U16_F "), IP packet dropped.\n",
			             iphdr_len,
			             p->tot_len));
		}
		/* free (drop) packet pbufs */
		pbuf_free(p);
		IP_STATS_INC(ip.lenerr);
		IP_STATS_INC(ip.drop);
		snmp_inc_ipindiscards();
		return ERR_OK;
	}

		/* verify checksum */
#if CHECKSUM_CHECK_IP
	if (inet_chksum(iphdr, iphdr_hlen) != 0) {

		LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
		            ("Checksum (0x%" X16_F ") failed, IP packet dropped.\n", inet_chksum(iphdr, iphdr_hlen)));
		ip_debug_print(p);
		pbuf_free(p);
		IP_STATS_INC(ip.chkerr);
		IP_STATS_INC(ip.drop);
		snmp_inc_ipinhdrerrors();
		return ERR_OK;
	}
#endif

	/* Trim pbuf. This should have been done at the netif layer,
	 * but we'll do it anyway just to be sure that its done. */
	pbuf_realloc(p, iphdr_len);

	/* copy IP addresses to aligned ip_addr_t */
	ip_addr_copy(current_iphdr_dest, iphdr->dest);
	ip_addr_copy(current_iphdr_src, iphdr->src);

	/* match packet against an interface, i.e. is this packet for us? */
#if LWIP_IGMP
	if (ip_addr_ismulticast(&current_iphdr_dest)) {
		if ((inp->flags & NETIF_FLAG_IGMP) && (igmp_lookfor_group(inp, &current_iphdr_dest))) {
			netif = inp;
		} else {
			netif = NULL;
		}
	} else
#endif /* LWIP_IGMP */
	{
		/* start trying with inp. if that's not acceptable, start walking the
		   list of configured netifs.
		   'first' is used as a boolean to mark whether we started walking the list */
		int first = 1;
		netif     = inp;
		do {
			LWIP_DEBUGF(IP_DEBUG,
			            ("ip_input: iphdr->dest 0x%" X32_F " netif->ip_addr 0x%" X32_F " (0x%" X32_F ", 0x%" X32_F
			             ", 0x%" X32_F ")\n",
			             ip4_addr_get_u32(&iphdr->dest),
			             ip4_addr_get_u32(&netif->ip_addr),
			             ip4_addr_get_u32(&iphdr->dest) & ip4_addr_get_u32(&netif->netmask),
			             ip4_addr_get_u32(&netif->ip_addr) & ip4_addr_get_u32(&netif->netmask),
			             ip4_addr_get_u32(&iphdr->dest) & ~ip4_addr_get_u32(&netif->netmask)));

			/* interface is up and configured? */
			if ((netif_is_up(netif)) && (!ip_addr_isany(&(netif->ip_addr)))) {
				/* unicast to this interface address? */
				if (ip_addr_cmp(&current_iphdr_dest, &(netif->ip_addr)) ||
				    /* or broadcast on this interface network address? */
				    ip_addr_isbroadcast(&current_iphdr_dest, netif)) {
					LWIP_DEBUGF(IP_DEBUG,
					            ("ip_input: packet accepted on interface %c%c\n", netif->name[0], netif->name[1]));
					/* break out of for loop */
					break;
				}
#if LWIP_AUTOIP
				/* connections to link-local addresses must persist after changing
				   the netif's address (RFC3927 ch. 1.9) */
				if ((netif->autoip != NULL) && ip_addr_cmp(&current_iphdr_dest, &(netif->autoip->llipaddr))) {
					LWIP_DEBUGF(IP_DEBUG,
					            ("ip_input: LLA packet accepted on interface %c%c\n", netif->name[0], netif->name[1]));
					/* break out of for loop */
					break;
				}
#endif /* LWIP_AUTOIP */
			}
			if (first) {
				first = 0;
				netif = netif_list;
			} else {
				netif = netif->next;
			}
			if (netif == inp) {
				netif = netif->next;
			}
		} while (netif != NULL);
	}

#if IP_ACCEPT_LINK_LAYER_ADDRESSING
	/* Pass DHCP messages regardless of destination address. DHCP traffic is addressed
	 * using link layer addressing (such as Ethernet MAC) so we must not filter on IP.
	 * According to RFC 1542 section 3.1.1, referred by RFC 2131).
	 *
	 * If you want to accept private broadcast communication while a netif is down,
	 * define LWIP_IP_ACCEPT_UDP_PORT(dst_port), e.g.:
	 *
	 * #define LWIP_IP_ACCEPT_UDP_PORT(dst_port) ((dst_port) == PP_NTOHS(12345))
	 */
	if (netif == NULL) {
		/* remote port is DHCP server? */
		if (IPH_PROTO(iphdr) == IP_PROTO_UDP) {
			struct udp_hdr *udphdr = (struct udp_hdr *)((u8_t *)iphdr + iphdr_hlen);
			LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE,
			            ("ip_input: UDP packet to DHCP client port %" U16_F "\n", ntohs(udphdr->dest)));
			if (IP_ACCEPT_LINK_LAYER_ADDRESSED_PORT(udphdr->dest)) {
				LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE, ("ip_input: DHCP packet accepted.\n"));
				netif        = inp;
				check_ip_src = 0;
			}
		}
	}
#endif /* IP_ACCEPT_LINK_LAYER_ADDRESSING */

		/* broadcast or multicast packet source address? Compliant with RFC 1122: 3.2.1.3 */
#if IP_ACCEPT_LINK_LAYER_ADDRESSING
	/* DHCP servers need 0.0.0.0 to be allowed as source address (RFC 1.1.2.2: 3.2.1.3/a) */
	if (check_ip_src && !ip_addr_isany(&current_iphdr_src))
#endif /* IP_ACCEPT_LINK_LAYER_ADDRESSING */
	{
		if ((ip_addr_isbroadcast(&current_iphdr_src, inp)) || (ip_addr_ismulticast(&current_iphdr_src))) {
			/* packet source is not valid */
			LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
			            ("ip_input: packet source is not valid.\n"));
			/* free (drop) packet pbufs */
			pbuf_free(p);
			IP_STATS_INC(ip.drop);
			snmp_inc_ipinaddrerrors();
			snmp_inc_ipindiscards();
			return ERR_OK;
		}
	}

	/* packet not for us? */
	if (netif == NULL) {
		/* packet not for us, route or discard */
		LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE, ("ip_input: packet not for us.\n"));
#if IP_FORWARD
		/* non-broadcast packet? */
		if (!ip_addr_isbroadcast(&current_iphdr_dest, inp)) {
			/* try to forward IP packet on (other) interfaces */
			ip_forward(p, iphdr, inp);
		} else
#endif /* IP_FORWARD */
		{
			snmp_inc_ipinaddrerrors();
			snmp_inc_ipindiscards();
		}
		pbuf_free(p);
		return ERR_OK;
	}
	/* packet consists of multiple fragments? */
	if ((IPH_OFFSET(iphdr) & PP_HTONS(IP_OFFMASK | IP_MF)) != 0) {
#if IP_REASSEMBLY /* packet fragment reassembly code present? */
		LWIP_DEBUGF(IP_DEBUG,
		            ("IP packet is a fragment (id=0x%04" X16_F " tot_len=%" U16_F " len=%" U16_F " MF=%" U16_F
		             " offset=%" U16_F "), calling ip_reass()\n",
		             ntohs(IPH_ID(iphdr)),
		             p->tot_len,
		             ntohs(IPH_LEN(iphdr)),
		             !!(IPH_OFFSET(iphdr) & PP_HTONS(IP_MF)),
		             (ntohs(IPH_OFFSET(iphdr)) & IP_OFFMASK) * 8));
		/* reassemble the packet*/
		p = ip_reass(p);
		/* packet not fully reassembled yet? */
		if (p == NULL) {
			return ERR_OK;
		}
		iphdr = (struct ip_hdr *)p->payload;
#else  /* IP_REASSEMBLY == 0, no packet fragment reassembly code present */
		pbuf_free(p);
		LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
		            ("IP packet dropped since it was fragmented (0x%" X16_F ") (while IP_REASSEMBLY == 0).\n",
		             ntohs(IPH_OFFSET(iphdr))));
		IP_STATS_INC(ip.opterr);
		IP_STATS_INC(ip.drop);
		/* unsupported protocol feature */
		snmp_inc_ipinunknownprotos();
		return ERR_OK;
#endif /* IP_REASSEMBLY */
	}

#if IP_OPTIONS_ALLOWED == 0 /* no support for IP options in the IP header? */

#if LWIP_IGMP
	/* there is an extra "router alert" option in IGMP messages which we allow for but do not police */
	if ((iphdr_hlen > IP_HLEN) && (IPH_PROTO(iphdr) != IP_PROTO_IGMP)) {
#else
	if (iphdr_hlen > IP_HLEN) {
#endif /* LWIP_IGMP */
		LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
		            ("IP packet dropped since there were IP options (while IP_OPTIONS_ALLOWED == 0).\n"));
		pbuf_free(p);
		IP_STATS_INC(ip.opterr);
		IP_STATS_INC(ip.drop);
		/* unsupported protocol feature */
		snmp_inc_ipinunknownprotos();
		return ERR_OK;
	}
#endif /* IP_OPTIONS_ALLOWED == 0 */

	/* send to upper layers */
	LWIP_DEBUGF(IP_DEBUG, ("ip_input: \n"));
	ip_debug_print(p);
	LWIP_DEBUGF(IP_DEBUG, ("ip_input: p->len %" U16_F " p->tot_len %" U16_F "\n", p->len, p->tot_len));

	current_netif  = inp;
	current_header = iphdr;

#if LWIP_RAW
	/* raw input did not eat the packet? */
	if (raw_input(p, inp) == 0)
#endif /* LWIP_RAW */
	{
		switch (IPH_PROTO(iphdr)) {
#if LWIP_UDP
		case IP_PROTO_UDP:
#if LWIP_UDPLITE
		case IP_PROTO_UDPLITE:
#endif /* LWIP_UDPLITE */
			snmp_inc_ipindelivers();
			udp_input(p, inp);
			break;
#endif /* LWIP_UDP */
#if LWIP_TCP
		case IP_PROTO_TCP:
			snmp_inc_ipindelivers();
			tcp_input(p, inp);
			break;
#endif /* LWIP_TCP */
#if LWIP_ICMP
		case IP_PROTO_ICMP:
			snmp_inc_ipindelivers();
			icmp_input(p, inp);
			break;
#endif /* LWIP_ICMP */
#if LWIP_IGMP
		case IP_PROTO_IGMP:
			igmp_input(p, inp, &current_iphdr_dest);
			break;
#endif /* LWIP_IGMP */
		default:
#if LWIP_ICMP
			/* send ICMP destination protocol unreachable unless is was a broadcast */
			if (!ip_addr_isbroadcast(&current_iphdr_dest, inp) && !ip_addr_ismulticast(&current_iphdr_dest)) {
				p->payload = iphdr;
				icmp_dest_unreach(p, ICMP_DUR_PROTO);
			}
#endif /* LWIP_ICMP */
			pbuf_free(p);

			LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
			            ("Unsupported transport protocol %" U16_F "\n", IPH_PROTO(iphdr)));

			IP_STATS_INC(ip.proterr);
			IP_STATS_INC(ip.drop);
			snmp_inc_ipinunknownprotos();
		}
	}

	current_netif  = NULL;
	current_header = NULL;
	ip_addr_set_any(&current_iphdr_src);
	ip_addr_set_any(&current_iphdr_dest);

	return ERR_OK;
}

/**
 * Sends an IP packet on a network interface. This function constructs
 * the IP header and calculates the IP header checksum. If the source
 * IP address is NULL, the IP address of the outgoing network
 * interface is filled in as source address.
 * If the destination IP address is IP_HDRINCL, p is assumed to already
 * include an IP header and p->payload points to it instead of the data.
 *
 * @param p the packet to send (p->payload points to the data, e.g. next
            protocol header; if dest == IP_HDRINCL, p already includes an IP
            header and p->payload points to that IP header)
 * @param src the source IP address to send from (if src == IP_ADDR_ANY, the
 *         IP  address of the netif used to send is used as source address)
 * @param dest the destination IP address to send the packet to
 * @param ttl the TTL value to be set in the IP header
 * @param tos the TOS value to be set in the IP header
 * @param proto the PROTOCOL to be set in the IP header
 * @param netif the netif on which to send this packet
 * @return ERR_OK if the packet was sent OK
 *         ERR_BUF if p doesn't have enough space for IP/LINK headers
 *         returns errors returned by netif->output
 *
 * @note ip_id: RFC791 "some host may be able to simply use
 *  unique identifiers independent of destination"
 */
err_t ip_output_if(struct pbuf *p, ip_addr_t *src, ip_addr_t *dest, u8_t ttl, u8_t tos, u8_t proto, struct netif *netif)
{
#if IP_OPTIONS_SEND
	return ip_output_if_opt(p, src, dest, ttl, tos, proto, netif, NULL, 0);
}

/**
 * Same as ip_output_if() but with the possibility to include IP options:
 *
 * @ param ip_options pointer to the IP options, copied into the IP header
 * @ param optlen length of ip_options
 */
err_t ip_output_if_opt(struct pbuf *p, ip_addr_t *src, ip_addr_t *dest, u8_t ttl, u8_t tos, u8_t proto,
                       struct netif *netif, void *ip_options, u16_t optlen)
{
#endif /* IP_OPTIONS_SEND */
	struct ip_hdr *iphdr;
	ip_addr_t      dest_addr;
#if CHECKSUM_GEN_IP_INLINE
	u32_t chk_sum = 0;
#endif /* CHECKSUM_GEN_IP_INLINE */

	/* pbufs passed to IP must have a ref-count of 1 as their payload pointer
	   gets altered as the packet is passed down the stack */
	LWIP_ASSERT("p->ref == 1", p->ref == 1);

	snmp_inc_ipoutrequests();

	/* Should the IP header be generated or is it already included in p? */
	if (dest != IP_HDRINCL) {
		u16_t ip_hlen = IP_HLEN;
#if IP_OPTIONS_SEND
		u16_t optlen_aligned = 0;
		if (optlen != 0) {
#if CHECKSUM_GEN_IP_INLINE
			int i;
#endif /* CHECKSUM_GEN_IP_INLINE */
			/* round up to a multiple of 4 */
			optlen_aligned = ((optlen + 3) & ~3);
			ip_hlen += optlen_aligned;
			/* First write in the IP options */
			if (pbuf_header(p, optlen_aligned)) {
				LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
				            ("ip_output_if_opt: not enough room for IP options in pbuf\n"));
				IP_STATS_INC(ip.err);
				snmp_inc_ipoutdiscards();
				return ERR_BUF;
			}
			MEMCPY(p->payload, ip_options, optlen);
			if (optlen < optlen_aligned) {
				/* zero the remaining bytes */
				memset(((char *)p->payload) + optlen, 0, optlen_aligned - optlen);
			}
#if CHECKSUM_GEN_IP_INLINE
			for (i = 0; i < optlen_aligned / 2; i++) {
				chk_sum += ((u16_t *)p->payload)[i];
			}
#endif /* CHECKSUM_GEN_IP_INLINE */
		}
#endif /* IP_OPTIONS_SEND */
		/* generate IP header */
		if (pbuf_header(p, IP_HLEN)) {
			LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("ip_output: not enough room for IP header in pbuf\n"));

			IP_STATS_INC(ip.err);
			snmp_inc_ipoutdiscards();
			return ERR_BUF;
		}

		iphdr = (struct ip_hdr *)p->payload;
		LWIP_ASSERT("check that first pbuf can hold struct ip_hdr", (p->len >= sizeof(struct ip_hdr)));

		IPH_TTL_SET(iphdr, ttl);
		IPH_PROTO_SET(iphdr, proto);
#if CHECKSUM_GEN_IP_INLINE
		chk_sum += LWIP_MAKE_U16(proto, ttl);
#endif /* CHECKSUM_GEN_IP_INLINE */

		/* dest cannot be NULL here */
		ip_addr_copy(iphdr->dest, *dest);
#if CHECKSUM_GEN_IP_INLINE
		chk_sum += ip4_addr_get_u32(&iphdr->dest) & 0xFFFF;
		chk_sum += ip4_addr_get_u32(&iphdr->dest) >> 16;
#endif /* CHECKSUM_GEN_IP_INLINE */

		IPH_VHL_SET(iphdr, 4, ip_hlen / 4);
		IPH_TOS_SET(iphdr, tos);
#if CHECKSUM_GEN_IP_INLINE
		chk_sum += LWIP_MAKE_U16(tos, iphdr->_v_hl);
#endif /* CHECKSUM_GEN_IP_INLINE */
		IPH_LEN_SET(iphdr, htons(p->tot_len));
#if CHECKSUM_GEN_IP_INLINE
		chk_sum += iphdr->_len;
#endif /* CHECKSUM_GEN_IP_INLINE */
		IPH_OFFSET_SET(iphdr, 0);
		IPH_ID_SET(iphdr, htons(ip_id));
#if CHECKSUM_GEN_IP_INLINE
		chk_sum += iphdr->_id;
#endif /* CHECKSUM_GEN_IP_INLINE */
		++ip_id;

		if (ip_addr_isany(src)) {
			ip_addr_copy(iphdr->src, netif->ip_addr);
		} else {
			/* src cannot be NULL here */
			ip_addr_copy(iphdr->src, *src);
		}

#if CHECKSUM_GEN_IP_INLINE
		chk_sum += ip4_addr_get_u32(&iphdr->src) & 0xFFFF;
		chk_sum += ip4_addr_get_u32(&iphdr->src) >> 16;
		chk_sum        = (chk_sum >> 16) + (chk_sum & 0xFFFF);
		chk_sum        = (chk_sum >> 16) + chk_sum;
		chk_sum        = ~chk_sum;
		iphdr->_chksum = chk_sum; /* network order */
#else                             /* CHECKSUM_GEN_IP_INLINE */
		IPH_CHKSUM_SET(iphdr, 0);
#if CHECKSUM_GEN_IP
		IPH_CHKSUM_SET(iphdr, inet_chksum(iphdr, ip_hlen));
#endif
#endif /* CHECKSUM_GEN_IP_INLINE */
	} else {
		/* IP header already included in p */
		iphdr = (struct ip_hdr *)p->payload;
		ip_addr_copy(dest_addr, iphdr->dest);
		dest = &dest_addr;
	}

	IP_STATS_INC(ip.xmit);

	LWIP_DEBUGF(IP_DEBUG, ("ip_output_if: %c%c%" U16_F "\n", netif->name[0], netif->name[1], netif->num));
	ip_debug_print(p);

#if ENABLE_LOOPBACK
	if (ip_addr_cmp(dest, &netif->ip_addr)) {
		/* Packet to self, enqueue it for loopback */
		LWIP_DEBUGF(IP_DEBUG, ("netif_loop_output()"));
		return netif_loop_output(netif, p, dest);
	}
#if LWIP_IGMP
	if ((p->flags & PBUF_FLAG_MCASTLOOP) != 0) {
		netif_loop_output(netif, p, dest);
	}
#endif /* LWIP_IGMP */
#endif /* ENABLE_LOOPBACK */
#if IP_FRAG
	/* don't fragment if interface has mtu set to 0 [loopif] */
	if (netif->mtu && (p->tot_len > netif->mtu)) {
		return ip_frag(p, netif, dest);
	}
#endif /* IP_FRAG */

	LWIP_DEBUGF(IP_DEBUG, ("netif->output()"));
	return netif->output(netif, p, dest);
}

/**
 * Simple interface to ip_output_if. It finds the outgoing network
 * interface and calls upon ip_output_if to do the actual work.
 *
 * @param p the packet to send (p->payload points to the data, e.g. next
            protocol header; if dest == IP_HDRINCL, p already includes an IP
            header and p->payload points to that IP header)
 * @param src the source IP address to send from (if src == IP_ADDR_ANY, the
 *         IP  address of the netif used to send is used as source address)
 * @param dest the destination IP address to send the packet to
 * @param ttl the TTL value to be set in the IP header
 * @param tos the TOS value to be set in the IP header
 * @param proto the PROTOCOL to be set in the IP header
 *
 * @return ERR_RTE if no route is found
 *         see ip_output_if() for more return values
 */
err_t ip_output(struct pbuf *p, ip_addr_t *src, ip_addr_t *dest, u8_t ttl, u8_t tos, u8_t proto)
{
	struct netif *netif;

	/* pbufs passed to IP must have a ref-count of 1 as their payload pointer
	   gets altered as the packet is passed down the stack */
	LWIP_ASSERT("p->ref == 1", p->ref == 1);

	if ((netif = ip_route(dest)) == NULL) {
		LWIP_DEBUGF(IP_DEBUG,
		            ("ip_output: No route to %" U16_F ".%" U16_F ".%" U16_F ".%" U16_F "\n",
		             ip4_addr1_16(dest),
		             ip4_addr2_16(dest),
		             ip4_addr3_16(dest),
		             ip4_addr4_16(dest)));
		IP_STATS_INC(ip.rterr);
		return ERR_RTE;
	}

	return ip_output_if(p, src, dest, ttl, tos, proto, netif);
}

#if LWIP_NETIF_HWADDRHINT
/** Like ip_output, but takes and addr_hint pointer that is passed on to netif->addr_hint
 *  before calling ip_output_if.
 *
 * @param p the packet to send (p->payload points to the data, e.g. next
            protocol header; if dest == IP_HDRINCL, p already includes an IP
            header and p->payload points to that IP header)
 * @param src the source IP address to send from (if src == IP_ADDR_ANY, the
 *         IP  address of the netif used to send is used as source address)
 * @param dest the destination IP address to send the packet to
 * @param ttl the TTL value to be set in the IP header
 * @param tos the TOS value to be set in the IP header
 * @param proto the PROTOCOL to be set in the IP header
 * @param addr_hint address hint pointer set to netif->addr_hint before
 *        calling ip_output_if()
 *
 * @return ERR_RTE if no route is found
 *         see ip_output_if() for more return values
 */
err_t ip_output_hinted(struct pbuf *p, ip_addr_t *src, ip_addr_t *dest, u8_t ttl, u8_t tos, u8_t proto, u8_t *addr_hint)
{
	struct netif *netif;
	err_t         err;

	/* pbufs passed to IP must have a ref-count of 1 as their payload pointer
	   gets altered as the packet is passed down the stack */
	LWIP_ASSERT("p->ref == 1", p->ref == 1);

	if ((netif = ip_route(dest)) == NULL) {
		LWIP_DEBUGF(IP_DEBUG,
		            ("ip_output: No route to %" U16_F ".%" U16_F ".%" U16_F ".%" U16_F "\n",
		             ip4_addr1_16(dest),
		             ip4_addr2_16(dest),
		             ip4_addr3_16(dest),
		             ip4_addr4_16(dest)));
		IP_STATS_INC(ip.rterr);
		return ERR_RTE;
	}

	NETIF_SET_HWADDRHINT(netif, addr_hint);
	err = ip_output_if(p, src, dest, ttl, tos, proto, netif);
	NETIF_SET_HWADDRHINT(netif, NULL);

	return err;
}
#endif /* LWIP_NETIF_HWADDRHINT*/

#if IP_DEBUG
/* Print an IP header by using LWIP_DEBUGF
 * @param p an IP packet, p->payload pointing to the IP header
 */
void ip_debug_print(struct pbuf *p)
{
	struct ip_hdr *iphdr = (struct ip_hdr *)p->payload;

	LWIP_DEBUGF(IP_DEBUG, ("IP header:\n"));
	LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
	LWIP_DEBUGF(IP_DEBUG,
	            ("|%2" S16_F " |%2" S16_F " |  0x%02" X16_F " |     %5" U16_F "     | (v, hl, tos, len)\n",
	             IPH_V(iphdr),
	             IPH_HL(iphdr),
	             IPH_TOS(iphdr),
	             ntohs(IPH_LEN(iphdr))));
	LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
	LWIP_DEBUGF(IP_DEBUG,
	            ("|    %5" U16_F "      |%" U16_F "%" U16_F "%" U16_F "|    %4" U16_F "   | (id, flags, offset)\n",
	             ntohs(IPH_ID(iphdr)),
	             ntohs(IPH_OFFSET(iphdr)) >> 15 & 1,
	             ntohs(IPH_OFFSET(iphdr)) >> 14 & 1,
	             ntohs(IPH_OFFSET(iphdr)) >> 13 & 1,
	             ntohs(IPH_OFFSET(iphdr)) & IP_OFFMASK));
	LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
	LWIP_DEBUGF(IP_DEBUG,
	            ("|  %3" U16_F "  |  %3" U16_F "  |    0x%04" X16_F "     | (ttl, proto, chksum)\n",
	             IPH_TTL(iphdr),
	             IPH_PROTO(iphdr),
	             ntohs(IPH_CHKSUM(iphdr))));
	LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
	LWIP_DEBUGF(IP_DEBUG,
	            ("|  %3" U16_F "  |  %3" U16_F "  |  %3" U16_F "  |  %3" U16_F "  | (src)\n",
	             ip4_addr1_16(&iphdr->src),
	             ip4_addr2_16(&iphdr->src),
	             ip4_addr3_16(&iphdr->src),
	             ip4_addr4_16(&iphdr->src)));
	LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
	LWIP_DEBUGF(IP_DEBUG,
	            ("|  %3" U16_F "  |  %3" U16_F "  |  %3" U16_F "  |  %3" U16_F "  | (dest)\n",
	             ip4_addr1_16(&iphdr->dest),
	             ip4_addr2_16(&iphdr->dest),
	             ip4_addr3_16(&iphdr->dest),
	             ip4_addr4_16(&iphdr->dest)));
	LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
}
#endif /* IP_DEBUG */
